//     Backbone.js 0.9.2

//     (c) 2010-2012 Jeremy Ashkenas, DocumentCloud Inc.
//     Backbone may be freely distributed under the MIT license.
//     For all details and documentation:
//     http://backbonejs.org

(function(){

    // Initial Setup
    // -------------

    // Save a reference to the global object (`window` in the browser, `global`
    // on the server).
    var root = this;

    // Save the previous value of the `Backbone` variable, so that it can be
    // restored later on, if `noConflict` is used.
    var previousBackbone = root.Backbone;

    // Create a local reference to slice/splice.
    var slice = Array.prototype.slice;
    var splice = Array.prototype.splice;

    // The top-level namespace. All public Backbone classes and modules will
    // be attached to this. Exported for both CommonJS and the browser.
    var Backbone;
    if (typeof exports !== 'undefined') {
        Backbone = exports;
    } else {
        Backbone = root.Backbone = {};
    }

    // Current version of the library. Keep in sync with `package.json`.
    Backbone.VERSION = '0.9.2';

    // Require Underscore, if we're on the server, and it's not already present.
    var _ = root._;
    if (!_ && (typeof require !== 'undefined')) _ = require('underscore');

    // For Backbone's purposes, jQuery, Zepto, or Ender owns the `$` variable.
    var $ = root.jQuery || root.Zepto || root.ender;

    // Set the JavaScript library that will be used for DOM manipulation and
    // Ajax calls (a.k.a. the `$` variable). By default Backbone will use: jQuery,
    // Zepto, or Ender; but the `setDomLibrary()` method lets you inject an
    // alternate JavaScript library (or a mock library for testing your views
    // outside of a browser).
    Backbone.setDomLibrary = function(lib) {
        $ = lib;
    };

    // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
    // to its previous owner. Returns a reference to this Backbone object.
    Backbone.noConflict = function() {
        root.Backbone = previousBackbone;
        return this;
    };

    // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option
    // will fake `"PUT"` and `"DELETE"` requests via the `_method` parameter and
    // set a `X-Http-Method-Override` header.
    Backbone.emulateHTTP = false;

    // Turn on `emulateJSON` to support legacy servers that can't deal with direct
    // `application/json` requests ... will encode the body as
    // `application/x-www-form-urlencoded` instead and will send the model in a
    // form param named `model`.
    Backbone.emulateJSON = false;

    // Backbone.Events
    // -----------------

    // Regular expression used to split event strings
    var eventSplitter = /\s+/;

    // A module that can be mixed in to *any object* in order to provide it with
    // custom events. You may bind with `on` or remove with `off` callback functions
    // to an event; trigger`-ing an event fires all callbacks in succession.
    //
    //     var object = {};
    //     _.extend(object, Backbone.Events);
    //     object.on('expand', function(){ alert('expanded'); });
    //     object.trigger('expand');
    //
    var Events = Backbone.Events = {

        // Bind one or more space separated events, `events`, to a `callback`
        // function. Passing `"all"` will bind the callback to all events fired.
        on: function(events, callback, context) {

            var calls, event, node, tail, list;
            if (!callback) return this;
            events = events.split(eventSplitter);
            calls = this._callbacks || (this._callbacks = {});

            // Create an immutable callback list, allowing traversal during
            // modification.  The tail is an empty object that will always be used
            // as the next node.
            while (event = events.shift()) {
                list = calls[event];
                node = list ? list.tail : {};
                node.next = tail = {};
                node.context = context;
                node.callback = callback;
                calls[event] = {tail: tail, next: list ? list.next : node};
            }

            return this;
        },

        // Remove one or many callbacks. If `context` is null, removes all callbacks
        // with that function. If `callback` is null, removes all callbacks for the
        // event. If `events` is null, removes all bound callbacks for all events.
        off: function(events, callback, context) {
            var event, calls, node, tail, cb, ctx;

            // No events, or removing *all* events.
            if (!(calls = this._callbacks)) return;
            if (!(events || callback || context)) {
                delete this._callbacks;
                return this;
            }

            // Loop through the listed events and contexts, splicing them out of the
            // linked list of callbacks if appropriate.
            events = events ? events.split(eventSplitter) : _.keys(calls);
            while (event = events.shift()) {
                node = calls[event];
                delete calls[event];
                if (!node || !(callback || context)) continue;
                // Create a new list, omitting the indicated callbacks.
                tail = node.tail;
                while ((node = node.next) !== tail) {
                    cb = node.callback;
                    ctx = node.context;
                    if ((callback && cb !== callback) || (context && ctx !== context)) {
                        this.on(event, cb, ctx);
                    }
                }
            }

            return this;
        },

        // Trigger one or many events, firing all bound callbacks. Callbacks are
        // passed the same arguments as `trigger` is, apart from the event name
        // (unless you're listening on `"all"`, which will cause your callback to
        // receive the true name of the event as the first argument).
        trigger: function(events) {
            var event, node, calls, tail, args, all, rest;
            if (!(calls = this._callbacks)) return this;
            all = calls.all;
            events = events.split(eventSplitter);
            rest = slice.call(arguments, 1);

            // For each event, walk through the linked list of callbacks twice,
            // first to trigger the event, then to trigger any `"all"` callbacks.
            while (event = events.shift()) {
                if (node = calls[event]) {
                    tail = node.tail;
                    while ((node = node.next) !== tail) {
                        node.callback.apply(node.context || this, rest);
                    }
                }
                if (node = all) {
                    tail = node.tail;
                    args = [event].concat(rest);
                    while ((node = node.next) !== tail) {
                        node.callback.apply(node.context || this, args);
                    }
                }
            }

            return this;
        }

    };

    // Aliases for backwards compatibility.
    Events.bind   = Events.on;
    Events.unbind = Events.off;

    // Backbone.Model
    // --------------

    // Create a new model, with defined attributes. A client id (`cid`)
    // is automatically generated and assigned for you.
    var Model = Backbone.Model = function(attributes, options) {
        var defaults;
        attributes || (attributes = {});
        if (options && options.parse) attributes = this.parse(attributes);
        if (defaults = getValue(this, 'defaults')) {
            attributes = _.extend({}, defaults, attributes);
        }
        if (options && options.collection) this.collection = options.collection;
        this.attributes = {};
        this._escapedAttributes = {};
        this.cid = _.uniqueId('c');
        this.changed = {};
        this._silent = {};
        this._pending = {};
        this.set(attributes, {silent: true});
        // Reset change tracking.
        this.changed = {};
        this._silent = {};
        this._pending = {};
        this._previousAttributes = _.clone(this.attributes);
        this.initialize.apply(this, arguments);
    };

    // Attach all inheritable methods to the Model prototype.
    _.extend(Model.prototype, Events, {

        // A hash of attributes whose current and previous value differ.
        changed: null,

        // A hash of attributes that have silently changed since the last time
        // `change` was called.  Will become pending attributes on the next call.
        _silent: null,

        // A hash of attributes that have changed since the last `'change'` event
        // began.
        _pending: null,

        // The default name for the JSON `id` attribute is `"id"`. MongoDB and
        // CouchDB users may want to set this to `"_id"`.
        idAttribute: 'id',

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},

        // Return a copy of the model's `attributes` object.
        toJSON: function(options) {
            return _.clone(this.attributes);
        },

        // Get the value of an attribute.
        get: function(attr) {
            return this.attributes[attr];
        },

        // Get the HTML-escaped value of an attribute.
        escape: function(attr) {
            var html;
            if (html = this._escapedAttributes[attr]) return html;
            var val = this.get(attr);
            return this._escapedAttributes[attr] = _.escape(val == null ? '' : '' + val);
        },

        // Returns `true` if the attribute contains a value that is not null
        // or undefined.
        has: function(attr) {
            return this.get(attr) != null;
        },

        // Set a hash of model attributes on the object, firing `"change"` unless
        // you choose to silence it.
        set: function(key, value, options) {
            var attrs, attr, val;

            // Handle both `"key", value` and `{key: value}` -style arguments.
            if (_.isObject(key) || key == null) {
                attrs = key;
                options = value;
            } else {
                attrs = {};
                attrs[key] = value;
            }

            // Extract attributes and options.
            options || (options = {});
            if (!attrs) return this;
            if (attrs instanceof Model) attrs = attrs.attributes;
            if (options.unset) for (attr in attrs) attrs[attr] = void 0;

            // Run validation.
            if (!this._validate(attrs, options)) return false;

            // Check for changes of `id`.
            if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];

            var changes = options.changes = {};
            var now = this.attributes;
            var escaped = this._escapedAttributes;
            var prev = this._previousAttributes || {};

            // For each `set` attribute...
            for (attr in attrs) {
                val = attrs[attr];

                // If the new and current value differ, record the change.
                if (!_.isEqual(now[attr], val) || (options.unset && _.has(now, attr))) {
                    delete escaped[attr];
                    (options.silent ? this._silent : changes)[attr] = true;
                }

                // Update or delete the current value.
                options.unset ? delete now[attr] : now[attr] = val;

                // If the new and previous value differ, record the change.  If not,
                // then remove changes for this attribute.
                if (!_.isEqual(prev[attr], val) || (_.has(now, attr) != _.has(prev, attr))) {
                    this.changed[attr] = val;
                    if (!options.silent) this._pending[attr] = true;
                } else {
                    delete this.changed[attr];
                    delete this._pending[attr];
                }
            }

            // Fire the `"change"` events.
            if (!options.silent) this.change(options);
            return this;
        },

        // Remove an attribute from the model, firing `"change"` unless you choose
        // to silence it. `unset` is a noop if the attribute doesn't exist.
        unset: function(attr, options) {
            (options || (options = {})).unset = true;
            return this.set(attr, null, options);
        },

        // Clear all attributes on the model, firing `"change"` unless you choose
        // to silence it.
        clear: function(options) {
            (options || (options = {})).unset = true;
            return this.set(_.clone(this.attributes), options);
        },

        // Fetch the model from the server. If the server's representation of the
        // model differs from its current attributes, they will be overriden,
        // triggering a `"change"` event.
        fetch: function(options) {
            options = options ? _.clone(options) : {};
            var model = this;
            var success = options.success;
            options.success = function(resp, status, xhr) {
                if (!model.set(model.parse(resp, xhr), options)) return false;
                if (success) success(model, resp);
            };
            options.error = Backbone.wrapError(options.error, model, options);
            return (this.sync || Backbone.sync).call(this, 'read', this, options);
        },

        // Set a hash of model attributes, and sync the model to the server.
        // If the server returns an attributes hash that differs, the model's
        // state will be `set` again.
        save: function(key, value, options) {
            var attrs, current;

            // Handle both `("key", value)` and `({key: value})` -style calls.
            if (_.isObject(key) || key == null) {
                attrs = key;
                options = value;
            } else {
                attrs = {};
                attrs[key] = value;
            }
            options = options ? _.clone(options) : {};

            // If we're "wait"-ing to set changed attributes, validate early.
            if (options.wait) {
                if (!this._validate(attrs, options)) return false;
                current = _.clone(this.attributes);
            }

            // Regular saves `set` attributes before persisting to the server.
            var silentOptions = _.extend({}, options, {silent: true});
            if (attrs && !this.set(attrs, options.wait ? silentOptions : options)) {
                return false;
            }

            // After a successful server-side save, the client is (optionally)
            // updated with the server-side state.
            var model = this;
            var success = options.success;
            options.success = function(resp, status, xhr) {
                var serverAttrs = model.parse(resp, xhr);
                if (options.wait) {
                    delete options.wait;
                    serverAttrs = _.extend(attrs || {}, serverAttrs);
                }
                if (!model.set(serverAttrs, options)) return false;
                if (success) {
                    success(model, resp);
                } else {
                    model.trigger('sync', model, resp, options);
                }
            };

            // Finish configuring and sending the Ajax request.
            options.error = Backbone.wrapError(options.error, model, options);
            var method = this.isNew() ? 'create' : 'update';
            var xhr = (this.sync || Backbone.sync).call(this, method, this, options);
            if (options.wait) this.set(current, silentOptions);
            return xhr;
        },

        // Destroy this model on the server if it was already persisted.
        // Optimistically removes the model from its collection, if it has one.
        // If `wait: true` is passed, waits for the server to respond before removal.
        destroy: function(options) {
            options = options ? _.clone(options) : {};
            var model = this;
            var success = options.success;

            var triggerDestroy = function() {
                model.trigger('destroy', model, model.collection, options);
            };

            if (this.isNew()) {
                triggerDestroy();
                return false;
            }

            options.success = function(resp) {
                if (options.wait) triggerDestroy();
                if (success) {
                    success(model, resp);
                } else {
                    model.trigger('sync', model, resp, options);
                }
            };

            options.error = Backbone.wrapError(options.error, model, options);
            var xhr = (this.sync || Backbone.sync).call(this, 'delete', this, options);
            if (!options.wait) triggerDestroy();
            return xhr;
        },

        // Default URL for the model's representation on the server -- if you're
        // using Backbone's restful methods, override this to change the endpoint
        // that will be called.
        url: function() {
            var base = getValue(this, 'urlRoot') || getValue(this.collection, 'url') || urlError();
            if (this.isNew()) return base;
            return base + (base.charAt(base.length - 1) == '/' ? '' : '/') + encodeURIComponent(this.id);
        },

        // **parse** converts a response into the hash of attributes to be `set` on
        // the model. The default implementation is just to pass the response along.
        parse: function(resp, xhr) {
            return resp;
        },

        // Create a new model with identical attributes to this one.
        clone: function() {
            return new this.constructor(this.attributes);
        },

        // A model is new if it has never been saved to the server, and lacks an id.
        isNew: function() {
            return this.id == null;
        },

        // Call this method to manually fire a `"change"` event for this model and
        // a `"change:attribute"` event for each changed attribute.
        // Calling this will cause all objects observing the model to update.
        change: function(options) {
            options || (options = {});
            var changing = this._changing;
            this._changing = true;

            // Silent changes become pending changes.
            for (var attr in this._silent) this._pending[attr] = true;

            // Silent changes are triggered.
            var changes = _.extend({}, options.changes, this._silent);
            this._silent = {};
            for (var attr in changes) {
                this.trigger('change:' + attr, this, this.get(attr), options);
            }
            if (changing) return this;

            // Continue firing `"change"` events while there are pending changes.
            while (!_.isEmpty(this._pending)) {
                this._pending = {};
                this.trigger('change', this, options);
                // Pending and silent changes still remain.
                for (var attr in this.changed) {
                    if (this._pending[attr] || this._silent[attr]) continue;
                    delete this.changed[attr];
                }
                this._previousAttributes = _.clone(this.attributes);
            }

            this._changing = false;
            return this;
        },

        // Determine if the model has changed since the last `"change"` event.
        // If you specify an attribute name, determine if that attribute has changed.
        hasChanged: function(attr) {
            if (!arguments.length) return !_.isEmpty(this.changed);
            return _.has(this.changed, attr);
        },

        // Return an object containing all the attributes that have changed, or
        // false if there are no changed attributes. Useful for determining what
        // parts of a view need to be updated and/or what attributes need to be
        // persisted to the server. Unset attributes will be set to undefined.
        // You can also pass an attributes object to diff against the model,
        // determining if there *would be* a change.
        changedAttributes: function(diff) {
            if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
            var val, changed = false, old = this._previousAttributes;
            for (var attr in diff) {
                if (_.isEqual(old[attr], (val = diff[attr]))) continue;
                (changed || (changed = {}))[attr] = val;
            }
            return changed;
        },

        // Get the previous value of an attribute, recorded at the time the last
        // `"change"` event was fired.
        previous: function(attr) {
            if (!arguments.length || !this._previousAttributes) return null;
            return this._previousAttributes[attr];
        },

        // Get all of the attributes of the model at the time of the previous
        // `"change"` event.
        previousAttributes: function() {
            return _.clone(this._previousAttributes);
        },

        // Check if the model is currently in a valid state. It's only possible to
        // get into an *invalid* state if you're using silent changes.
        isValid: function() {
            return !this.validate(this.attributes);
        },

        // Run validation against the next complete set of model attributes,
        // returning `true` if all is well. If a specific `error` callback has
        // been passed, call that instead of firing the general `"error"` event.
        _validate: function(attrs, options) {
            if (options.silent || !this.validate) return true;
            attrs = _.extend({}, this.attributes, attrs);
            var error = this.validate(attrs, options);
            if (!error) return true;
            if (options && options.error) {
                options.error(this, error, options);
            } else {
                this.trigger('error', this, error, options);
            }
            return false;
        }

    });

    // Backbone.Collection
    // -------------------

    // Provides a standard collection class for our sets of models, ordered
    // or unordered. If a `comparator` is specified, the Collection will maintain
    // its models in sort order, as they're added and removed.
    var Collection = Backbone.Collection = function(models, options) {
        options || (options = {});
        if (options.model) this.model = options.model;
        if (options.comparator) this.comparator = options.comparator;
        this._reset();
        this.initialize.apply(this, arguments);
        if (models) this.reset(models, {silent: true, parse: options.parse});
    };

    // Define the Collection's inheritable methods.
    _.extend(Collection.prototype, Events, {

        // The default model for a collection is just a **Backbone.Model**.
        // This should be overridden in most cases.
        model: Model,

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},

        // The JSON representation of a Collection is an array of the
        // models' attributes.
        toJSON: function(options) {
            return this.map(function(model){ return model.toJSON(options); });
        },

        // Add a model, or list of models to the set. Pass **silent** to avoid
        // firing the `add` event for every new model.
        add: function(models, options) {
            var i, index, length, model, cid, id, cids = {}, ids = {}, dups = [];
            options || (options = {});
            models = _.isArray(models) ? models.slice() : [models];

            // Begin by turning bare objects into model references, and preventing
            // invalid models or duplicate models from being added.
            for (i = 0, length = models.length; i < length; i++) {
                if (!(model = models[i] = this._prepareModel(models[i], options))) {
                    throw new Error("Can't add an invalid model to a collection");
                }
                cid = model.cid;
                id = model.id;
                if (cids[cid] || this._byCid[cid] || ((id != null) && (ids[id] || this._byId[id]))) {
                    dups.push(i);
                    continue;
                }
                cids[cid] = ids[id] = model;
            }

            // Remove duplicates.
            i = dups.length;
            while (i--) {
                models.splice(dups[i], 1);
            }

            // Listen to added models' events, and index models for lookup by
            // `id` and by `cid`.
            for (i = 0, length = models.length; i < length; i++) {
                (model = models[i]).on('all', this._onModelEvent, this);
                this._byCid[model.cid] = model;
                if (model.id != null) this._byId[model.id] = model;
            }

            // Insert models into the collection, re-sorting if needed, and triggering
            // `add` events unless silenced.
            this.length += length;
            index = options.at != null ? options.at : this.models.length;
            splice.apply(this.models, [index, 0].concat(models));
            if (this.comparator) this.sort({silent: true});
            if (options.silent) return this;
            for (i = 0, length = this.models.length; i < length; i++) {
                if (!cids[(model = this.models[i]).cid]) continue;
                options.index = i;
                model.trigger('add', model, this, options);
            }
            return this;
        },

        // Remove a model, or a list of models from the set. Pass silent to avoid
        // firing the `remove` event for every model removed.
        remove: function(models, options) {
            var i, l, index, model;
            options || (options = {});
            models = _.isArray(models) ? models.slice() : [models];
            for (i = 0, l = models.length; i < l; i++) {
                model = this.getByCid(models[i]) || this.get(models[i]);
                if (!model) continue;
                delete this._byId[model.id];
                delete this._byCid[model.cid];
                index = this.indexOf(model);
                this.models.splice(index, 1);
                this.length--;
                if (!options.silent) {
                    options.index = index;
                    model.trigger('remove', model, this, options);
                }
                this._removeReference(model);
            }
            return this;
        },

        // Add a model to the end of the collection.
        push: function(model, options) {
            model = this._prepareModel(model, options);
            this.add(model, options);
            return model;
        },

        // Remove a model from the end of the collection.
        pop: function(options) {
            var model = this.at(this.length - 1);
            this.remove(model, options);
            return model;
        },

        // Add a model to the beginning of the collection.
        unshift: function(model, options) {
            model = this._prepareModel(model, options);
            this.add(model, _.extend({at: 0}, options));
            return model;
        },

        // Remove a model from the beginning of the collection.
        shift: function(options) {
            var model = this.at(0);
            this.remove(model, options);
            return model;
        },

        // Get a model from the set by id.
        get: function(id) {
            if (id == null) return void 0;
            return this._byId[id.id != null ? id.id : id];
        },

        // Get a model from the set by client id.
        getByCid: function(cid) {
            return cid && this._byCid[cid.cid || cid];
        },

        // Get the model at the given index.
        at: function(index) {
            return this.models[index];
        },

        // Return models with matching attributes. Useful for simple cases of `filter`.
        where: function(attrs) {
            if (_.isEmpty(attrs)) return [];
            return this.filter(function(model) {
                for (var key in attrs) {
                    if (attrs[key] !== model.get(key)) return false;
                }
                return true;
            });
        },

        // Force the collection to re-sort itself. You don't need to call this under
        // normal circumstances, as the set will maintain sort order as each item
        // is added.
        sort: function(options) {
            options || (options = {});
            if (!this.comparator) throw new Error('Cannot sort a set without a comparator');
            var boundComparator = _.bind(this.comparator, this);
            if (this.comparator.length == 1) {
                this.models = this.sortBy(boundComparator);
            } else {
                this.models.sort(boundComparator);
            }
            if (!options.silent) this.trigger('reset', this, options);
            return this;
        },

        // Pluck an attribute from each model in the collection.
        pluck: function(attr) {
            return _.map(this.models, function(model){ return model.get(attr); });
        },

        // When you have more items than you want to add or remove individually,
        // you can reset the entire set with a new list of models, without firing
        // any `add` or `remove` events. Fires `reset` when finished.
        reset: function(models, options) {
            models  || (models = []);
            options || (options = {});
            for (var i = 0, l = this.models.length; i < l; i++) {
                this._removeReference(this.models[i]);
            }
            this._reset();
            this.add(models, _.extend({silent: true}, options));
            if (!options.silent) this.trigger('reset', this, options);
            return this;
        },

        // Fetch the default set of models for this collection, resetting the
        // collection when they arrive. If `add: true` is passed, appends the
        // models to the collection instead of resetting.
        fetch: function(options) {
            options = options ? _.clone(options) : {};
            if (options.parse === undefined) options.parse = true;
            var collection = this;
            var success = options.success;
            options.success = function(resp, status, xhr) {
                collection[options.add ? 'add' : 'reset'](collection.parse(resp, xhr), options);
                if (success) success(collection, resp);
            };
            options.error = Backbone.wrapError(options.error, collection, options);
            return (this.sync || Backbone.sync).call(this, 'read', this, options);
        },

        // Create a new instance of a model in this collection. Add the model to the
        // collection immediately, unless `wait: true` is passed, in which case we
        // wait for the server to agree.
        create: function(model, options) {
            var coll = this;
            options = options ? _.clone(options) : {};
            model = this._prepareModel(model, options);
            if (!model) return false;
            if (!options.wait) coll.add(model, options);
            var success = options.success;
            options.success = function(nextModel, resp, xhr) {
                if (options.wait) coll.add(nextModel, options);
                if (success) {
                    success(nextModel, resp);
                } else {
                    nextModel.trigger('sync', model, resp, options);
                }
            };
            model.save(null, options);
            return model;
        },

        // **parse** converts a response into a list of models to be added to the
        // collection. The default implementation is just to pass it through.
        parse: function(resp, xhr) {
            return resp;
        },

        // Proxy to _'s chain. Can't be proxied the same way the rest of the
        // underscore methods are proxied because it relies on the underscore
        // constructor.
        chain: function () {
            return _(this.models).chain();
        },

        // Reset all internal state. Called when the collection is reset.
        _reset: function(options) {
            this.length = 0;
            this.models = [];
            this._byId  = {};
            this._byCid = {};
        },

        // Prepare a model or hash of attributes to be added to this collection.
        _prepareModel: function(model, options) {
            options || (options = {});
            if (!(model instanceof Model)) {
                var attrs = model;
                options.collection = this;
                model = new this.model(attrs, options);
                if (!model._validate(model.attributes, options)) model = false;
            } else if (!model.collection) {
                model.collection = this;
            }
            return model;
        },

        // Internal method to remove a model's ties to a collection.
        _removeReference: function(model) {
            if (this == model.collection) {
                delete model.collection;
            }
            model.off('all', this._onModelEvent, this);
        },

        // Internal method called every time a model in the set fires an event.
        // Sets need to update their indexes when models change ids. All other
        // events simply proxy through. "add" and "remove" events that originate
        // in other collections are ignored.
        _onModelEvent: function(event, model, collection, options) {
            if ((event == 'add' || event == 'remove') && collection != this) return;
            if (event == 'destroy') {
                this.remove(model, options);
            }
            if (model && event === 'change:' + model.idAttribute) {
                delete this._byId[model.previous(model.idAttribute)];
                this._byId[model.id] = model;
            }
            this.trigger.apply(this, arguments);
        }

    });

    // Underscore methods that we want to implement on the Collection.
    var methods = ['forEach', 'each', 'map', 'reduce', 'reduceRight', 'find',
        'detect', 'filter', 'select', 'reject', 'every', 'all', 'some', 'any',
        'include', 'contains', 'invoke', 'max', 'min', 'sortBy', 'sortedIndex',
        'toArray', 'size', 'first', 'initial', 'rest', 'last', 'without', 'indexOf',
        'shuffle', 'lastIndexOf', 'isEmpty', 'groupBy'];

    // Mix in each Underscore method as a proxy to `Collection#models`.
    _.each(methods, function(method) {
        Collection.prototype[method] = function() {
            return _[method].apply(_, [this.models].concat(_.toArray(arguments)));
        };
    });

    // Backbone.Router
    // -------------------

    // Routers map faux-URLs to actions, and fire events when routes are
    // matched. Creating a new one sets its `routes` hash, if not set statically.
    var Router = Backbone.Router = function(options) {
        options || (options = {});
        if (options.routes) this.routes = options.routes;
        this._bindRoutes();
        this.initialize.apply(this, arguments);
    };

    // Cached regular expressions for matching named param parts and splatted
    // parts of route strings.
    var namedParam    = /:\w+/g;
    var splatParam    = /\*\w+/g;
    var escapeRegExp  = /[-[\]{}()+?.,\\^$|#\s]/g;

    // Set up all inheritable **Backbone.Router** properties and methods.
    _.extend(Router.prototype, Events, {

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},

        // Manually bind a single named route to a callback. For example:
        //
        //     this.route('search/:query/p:num', 'search', function(query, num) {
        //       ...
        //     });
        //
        route: function(route, name, callback) {
            Backbone.history || (Backbone.history = new History);
            if (!_.isRegExp(route)) route = this._routeToRegExp(route);
            if (!callback) callback = this[name];
            Backbone.history.route(route, _.bind(function(fragment) {
                var args = this._extractParameters(route, fragment);
                callback && callback.apply(this, args);
                this.trigger.apply(this, ['route:' + name].concat(args));
                Backbone.history.trigger('route', this, name, args);
            }, this));
            return this;
        },

        // Simple proxy to `Backbone.history` to save a fragment into the history.
        navigate: function(fragment, options) {
            Backbone.history.navigate(fragment, options);
        },

        // Bind all defined routes to `Backbone.history`. We have to reverse the
        // order of the routes here to support behavior where the most general
        // routes can be defined at the bottom of the route map.
        _bindRoutes: function() {
            if (!this.routes) return;
            var routes = [];
            for (var route in this.routes) {
                routes.unshift([route, this.routes[route]]);
            }
            for (var i = 0, l = routes.length; i < l; i++) {
                this.route(routes[i][0], routes[i][1], this[routes[i][1]]);
            }
        },

        // Convert a route string into a regular expression, suitable for matching
        // against the current location hash.
        _routeToRegExp: function(route) {
            route = route.replace(escapeRegExp, '\\$&')
                .replace(namedParam, '([^\/]+)')
                .replace(splatParam, '(.*?)');
            return new RegExp('^' + route + '$');
        },

        // Given a route, and a URL fragment that it matches, return the array of
        // extracted parameters.
        _extractParameters: function(route, fragment) {
            return route.exec(fragment).slice(1);
        }

    });

    // Backbone.History
    // ----------------

    // Handles cross-browser history management, based on URL fragments. If the
    // browser does not support `onhashchange`, falls back to polling.
    var History = Backbone.History = function() {
        this.handlers = [];
        _.bindAll(this, 'checkUrl');
    };

    // Cached regex for cleaning leading hashes and slashes .
    var routeStripper = /^[#\/]/;

    // Cached regex for detecting MSIE.
    var isExplorer = /msie [\w.]+/;

    // Has the history handling already been started?
    History.started = false;

    // Set up all inheritable **Backbone.History** properties and methods.
    _.extend(History.prototype, Events, {

        // The default interval to poll for hash changes, if necessary, is
        // twenty times a second.
        interval: 50,

        // Gets the true hash value. Cannot use location.hash directly due to bug
        // in Firefox where location.hash will always be decoded.
        getHash: function(windowOverride) {
            var loc = windowOverride ? windowOverride.location : window.location;
            var match = loc.href.match(/#(.*)$/);
            return match ? match[1] : '';
        },

        // Get the cross-browser normalized URL fragment, either from the URL,
        // the hash, or the override.
        getFragment: function(fragment, forcePushState) {
            if (fragment == null) {
                if (this._hasPushState || forcePushState) {
                    fragment = window.location.pathname;
                    var search = window.location.search;
                    if (search) fragment += search;
                } else {
                    fragment = this.getHash();
                }
            }
            if (!fragment.indexOf(this.options.root)) fragment = fragment.substr(this.options.root.length);
            return fragment.replace(routeStripper, '');
        },

        // Start the hash change handling, returning `true` if the current URL matches
        // an existing route, and `false` otherwise.
        start: function(options) {
            if (History.started) throw new Error("Backbone.history has already been started");
            History.started = true;

            // Figure out the initial configuration. Do we need an iframe?
            // Is pushState desired ... is it available?
            this.options          = _.extend({}, {root: '/'}, this.options, options);
            this._wantsHashChange = this.options.hashChange !== false;
            this._wantsPushState  = !!this.options.pushState;
            this._hasPushState    = !!(this.options.pushState && window.history && window.history.pushState);
            var fragment          = this.getFragment();
            var docMode           = document.documentMode;
            var oldIE             = (isExplorer.exec(navigator.userAgent.toLowerCase()) && (!docMode || docMode <= 7));

            if (oldIE) {
                this.iframe = $('<iframe src="javascript:0" tabindex="-1" />').hide().appendTo('body')[0].contentWindow;
                this.navigate(fragment);
            }

            // Depending on whether we're using pushState or hashes, and whether
            // 'onhashchange' is supported, determine how we check the URL state.
            if (this._hasPushState) {
                $(window).bind('popstate', this.checkUrl);
            } else if (this._wantsHashChange && ('onhashchange' in window) && !oldIE) {
                $(window).bind('hashchange', this.checkUrl);
            } else if (this._wantsHashChange) {
                this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
            }

            // Determine if we need to change the base url, for a pushState link
            // opened by a non-pushState browser.
            this.fragment = fragment;
            var loc = window.location;
            var atRoot  = loc.pathname == this.options.root;

            // If we've started off with a route from a `pushState`-enabled browser,
            // but we're currently in a browser that doesn't support it...
            if (this._wantsHashChange && this._wantsPushState && !this._hasPushState && !atRoot) {
                this.fragment = this.getFragment(null, true);
                window.location.replace(this.options.root + '#' + this.fragment);
                // Return immediately as browser will do redirect to new url
                return true;

                // Or if we've started out with a hash-based route, but we're currently
                // in a browser where it could be `pushState`-based instead...
            } else if (this._wantsPushState && this._hasPushState && atRoot && loc.hash) {
                this.fragment = this.getHash().replace(routeStripper, '');
                window.history.replaceState({}, document.title, loc.protocol + '//' + loc.host + this.options.root + this.fragment);
            }

            if (!this.options.silent) {
                return this.loadUrl();
            }
        },

        // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
        // but possibly useful for unit testing Routers.
        stop: function() {
            $(window).unbind('popstate', this.checkUrl).unbind('hashchange', this.checkUrl);
            clearInterval(this._checkUrlInterval);
            History.started = false;
        },

        // Add a route to be tested when the fragment changes. Routes added later
        // may override previous routes.
        route: function(route, callback) {
            this.handlers.unshift({route: route, callback: callback});
        },

        // Checks the current URL to see if it has changed, and if it has,
        // calls `loadUrl`, normalizing across the hidden iframe.
        checkUrl: function(e) {
            var current = this.getFragment();
            if (current == this.fragment && this.iframe) current = this.getFragment(this.getHash(this.iframe));
            if (current == this.fragment) return false;
            if (this.iframe) this.navigate(current);
            this.loadUrl() || this.loadUrl(this.getHash());
        },

        // Attempt to load the current URL fragment. If a route succeeds with a
        // match, returns `true`. If no defined routes matches the fragment,
        // returns `false`.
        loadUrl: function(fragmentOverride) {
            var fragment = this.fragment = this.getFragment(fragmentOverride);
            var matched = _.any(this.handlers, function(handler) {
                if (handler.route.test(fragment)) {
                    handler.callback(fragment);
                    return true;
                }
            });
            return matched;
        },

        // Save a fragment into the hash history, or replace the URL state if the
        // 'replace' option is passed. You are responsible for properly URL-encoding
        // the fragment in advance.
        //
        // The options object can contain `trigger: true` if you wish to have the
        // route callback be fired (not usually desirable), or `replace: true`, if
        // you wish to modify the current URL without adding an entry to the history.
        navigate: function(fragment, options) {
            if (!History.started) return false;
            if (!options || options === true) options = {trigger: options};
            var frag = (fragment || '').replace(routeStripper, '');
            if (this.fragment == frag) return;

            // If pushState is available, we use it to set the fragment as a real URL.
            if (this._hasPushState) {
                if (frag.indexOf(this.options.root) != 0) frag = this.options.root + frag;
                this.fragment = frag;
                window.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, frag);

                // If hash changes haven't been explicitly disabled, update the hash
                // fragment to store history.
            } else if (this._wantsHashChange) {
                this.fragment = frag;
                this._updateHash(window.location, frag, options.replace);
                if (this.iframe && (frag != this.getFragment(this.getHash(this.iframe)))) {
                    // Opening and closing the iframe tricks IE7 and earlier to push a history entry on hash-tag change.
                    // When replace is true, we don't want this.
                    if(!options.replace) this.iframe.document.open().close();
                    this._updateHash(this.iframe.location, frag, options.replace);
                }

                // If you've told us that you explicitly don't want fallback hashchange-
                // based history, then `navigate` becomes a page refresh.
            } else {
                window.location.assign(this.options.root + fragment);
            }
            if (options.trigger) this.loadUrl(fragment);
        },

        // Update the hash location, either replacing the current entry, or adding
        // a new one to the browser history.
        _updateHash: function(location, fragment, replace) {
            if (replace) {
                location.replace(location.toString().replace(/(javascript:|#).*$/, '') + '#' + fragment);
            } else {
                location.hash = fragment;
            }
        }
    });

    // Backbone.View
    // -------------

    // Creating a Backbone.View creates its initial element outside of the DOM,
    // if an existing element is not provided...
    var View = Backbone.View = function(options) {
        this.cid = _.uniqueId('view');
        this._configure(options || {});
        this._ensureElement();
        this.initialize.apply(this, arguments);
        this.delegateEvents();
    };

    // Cached regex to split keys for `delegate`.
    var delegateEventSplitter = /^(\S+)\s*(.*)$/;

    // List of view options to be merged as properties.
    var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName'];

    // Set up all inheritable **Backbone.View** properties and methods.
    _.extend(View.prototype, Events, {

        // The default `tagName` of a View's element is `"div"`.
        tagName: 'div',

        // jQuery delegate for element lookup, scoped to DOM elements within the
        // current view. This should be prefered to global lookups where possible.
        $: function(selector) {
            return this.$el.find(selector);
        },

        // Initialize is an empty function by default. Override it with your own
        // initialization logic.
        initialize: function(){},

        // **render** is the core function that your view should override, in order
        // to populate its element (`this.el`), with the appropriate HTML. The
        // convention is for **render** to always return `this`.
        render: function() {
            return this;
        },

        // Remove this view from the DOM. Note that the view isn't present in the
        // DOM by default, so calling this method may be a no-op.
        remove: function() {
            this.$el.remove();
            return this;
        },

        // For small amounts of DOM Elements, where a full-blown template isn't
        // needed, use **make** to manufacture elements, one at a time.
        //
        //     var el = this.make('li', {'class': 'row'}, this.model.escape('title'));
        //
        make: function(tagName, attributes, content) {
            var el = document.createElement(tagName);
            if (attributes) $(el).attr(attributes);
            if (content) $(el).html(content);
            return el;
        },

        // Change the view's element (`this.el` property), including event
        // re-delegation.
        setElement: function(element, delegate) {
            if (this.$el) this.undelegateEvents();
            this.$el = (element instanceof $) ? element : $(element);
            this.el = this.$el[0];
            if (delegate !== false) this.delegateEvents();
            return this;
        },

        // Set callbacks, where `this.events` is a hash of
        //
        // *{"event selector": "callback"}*
        //
        //     {
        //       'mousedown .title':  'edit',
        //       'click .button':     'save'
        //       'click .open':       function(e) { ... }
        //     }
        //
        // pairs. Callbacks will be bound to the view, with `this` set properly.
        // Uses event delegation for efficiency.
        // Omitting the selector binds the event to `this.el`.
        // This only works for delegate-able events: not `focus`, `blur`, and
        // not `change`, `submit`, and `reset` in Internet Explorer.
        delegateEvents: function(events) {
            if (!(events || (events = getValue(this, 'events')))) return;
            this.undelegateEvents();
            for (var key in events) {
                var method = events[key];
                if (!_.isFunction(method)) method = this[events[key]];
                if (!method) throw new Error('Method "' + events[key] + '" does not exist');
                var match = key.match(delegateEventSplitter);
                var eventName = match[1], selector = match[2];
                method = _.bind(method, this);
                eventName += '.delegateEvents' + this.cid;
                if (selector === '') {
                    this.$el.bind(eventName, method);
                } else {
                    this.$el.delegate(selector, eventName, method);
                }
            }
        },

        // Clears all callbacks previously bound to the view with `delegateEvents`.
        // You usually don't need to use this, but may wish to if you have multiple
        // Backbone views attached to the same DOM element.
        undelegateEvents: function() {
            this.$el.unbind('.delegateEvents' + this.cid);
        },

        // Performs the initial configuration of a View with a set of options.
        // Keys with special meaning *(model, collection, id, className)*, are
        // attached directly to the view.
        _configure: function(options) {
            if (this.options) options = _.extend({}, this.options, options);
            for (var i = 0, l = viewOptions.length; i < l; i++) {
                var attr = viewOptions[i];
                if (options[attr]) this[attr] = options[attr];
            }
            this.options = options;
        },

        // Ensure that the View has a DOM element to render into.
        // If `this.el` is a string, pass it through `$()`, take the first
        // matching element, and re-assign it to `el`. Otherwise, create
        // an element from the `id`, `className` and `tagName` properties.
        _ensureElement: function() {
            if (!this.el) {
                var attrs = getValue(this, 'attributes') || {};
                if (this.id) attrs.id = this.id;
                if (this.className) attrs['class'] = this.className;
                this.setElement(this.make(this.tagName, attrs), false);
            } else {
                this.setElement(this.el, false);
            }
        }

    });

    // The self-propagating extend function that Backbone classes use.
    var extend = function (protoProps, classProps) {
        var child = inherits(this, protoProps, classProps);
        child.extend = this.extend;
        return child;
    };

    // Set up inheritance for the model, collection, and view.
    Model.extend = Collection.extend = Router.extend = View.extend = extend;

    // Backbone.sync
    // -------------

    // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
    var methodMap = {
        'create': 'POST',
        'update': 'PUT',
        'delete': 'DELETE',
        'read':   'GET'
    };

    // Override this function to change the manner in which Backbone persists
    // models to the server. You will be passed the type of request, and the
    // model in question. By default, makes a RESTful Ajax request
    // to the model's `url()`. Some possible customizations could be:
    //
    // * Use `setTimeout` to batch rapid-fire updates into a single request.
    // * Send up the models as XML instead of JSON.
    // * Persist models via WebSockets instead of Ajax.
    //
    // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
    // as `POST`, with a `_method` parameter containing the true HTTP method,
    // as well as all requests with the body as `application/x-www-form-urlencoded`
    // instead of `application/json` with the model in a param named `model`.
    // Useful when interfacing with server-side languages like **PHP** that make
    // it difficult to read the body of `PUT` requests.
    Backbone.sync = function(method, model, options) {
        var type = methodMap[method];

        // Default options, unless specified.
        options || (options = {});

        // Default JSON-request options.
        var params = {type: type, dataType: 'json'};

        // Ensure that we have a URL.
        if (!options.url) {
            params.url = getValue(model, 'url') || urlError();
        }

        // Ensure that we have the appropriate request data.
        if (!options.data && model && (method == 'create' || method == 'update')) {
            params.contentType = 'application/json';
            params.data = JSON.stringify(model.toJSON());
        }

        // For older servers, emulate JSON by encoding the request into an HTML-form.
        if (Backbone.emulateJSON) {
            params.contentType = 'application/x-www-form-urlencoded';
            params.data = params.data ? {model: params.data} : {};
        }

        // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
        // And an `X-HTTP-Method-Override` header.
        if (Backbone.emulateHTTP) {
            if (type === 'PUT' || type === 'DELETE') {
                if (Backbone.emulateJSON) params.data._method = type;
                params.type = 'POST';
                params.beforeSend = function(xhr) {
                    xhr.setRequestHeader('X-HTTP-Method-Override', type);
                };
            }
        }

        // Don't process data on a non-GET request.
        if (params.type !== 'GET' && !Backbone.emulateJSON) {
            params.processData = false;
        }

        // Make the request, allowing the user to override any Ajax options.
        return $.ajax(_.extend(params, options));
    };

    // Wrap an optional error callback with a fallback error event.
    Backbone.wrapError = function(onError, originalModel, options) {
        return function(model, resp) {
            resp = model === originalModel ? resp : model;
            if (onError) {
                onError(originalModel, resp, options);
            } else {
                originalModel.trigger('error', originalModel, resp, options);
            }
        };
    };

    // Helpers
    // -------

    // Shared empty constructor function to aid in prototype-chain creation.
    var ctor = function(){};

    // Helper function to correctly set up the prototype chain, for subclasses.
    // Similar to `goog.inherits`, but uses a hash of prototype properties and
    // class properties to be extended.
    var inherits = function(parent, protoProps, staticProps) {
        var child;

        // The constructor function for the new subclass is either defined by you
        // (the "constructor" property in your `extend` definition), or defaulted
        // by us to simply call the parent's constructor.
        if (protoProps && protoProps.hasOwnProperty('constructor')) {
            child = protoProps.constructor;
        } else {
            child = function(){ parent.apply(this, arguments); };
        }

        // Inherit class (static) properties from parent.
        _.extend(child, parent);

        // Set the prototype chain to inherit from `parent`, without calling
        // `parent`'s constructor function.
        ctor.prototype = parent.prototype;
        child.prototype = new ctor();

        // Add prototype properties (instance properties) to the subclass,
        // if supplied.
        if (protoProps) _.extend(child.prototype, protoProps);

        // Add static properties to the constructor function, if supplied.
        if (staticProps) _.extend(child, staticProps);

        // Correctly set child's `prototype.constructor`.
        child.prototype.constructor = child;

        // Set a convenience property in case the parent's prototype is needed later.
        child.__super__ = parent.prototype;

        return child;
    };

    // Helper function to get a value from a Backbone object as a property
    // or as a function.
    var getValue = function(object, prop) {
        if (!(object && object[prop])) return null;
        return _.isFunction(object[prop]) ? object[prop]() : object[prop];
    };

    // Throw an error when a URL is needed, and none is supplied.
    var urlError = function() {
        throw new Error('A "url" property or function must be specified');
    };

}).call(this);